Well you have influence you use to get priority when you gonna buy stuff from nations for example:
I'm Germany and want to trade with Romanaia for oil however I only have 200 influence while USSR has 400
What this means is that the USSR gets to buy oil first that Romania provides to the world market. Lets say Romania provide 50 oil to the world market and USSR buys 40 of that with civilian factories (which you use to buy any resource) then I can only buy the remaining 10. Economy laws also play into this about how much a nation provides to the world market.
Also you can only control your import, you have 0 control over your export
I hope this clears things up for you.
